The present invention relates to a copper foil having a surface-treated layer for producing printed wiring boards and to a method for producing the copper foil.
Conventionally, copper foil has been employed as a material for producing printed wiring boards, which are widely used in the electric and electronics industries. In general, copper foil is bonded, through hot-pressing, onto an electrically insulating polymer material substrate such as glass-epoxy substrate, phenolic polymer substrate, or polyimide, to thereby form a copper-clad laminate, and the thus-prepared laminate is used for producing printed wiring boards.
In this connection, at least one side of a copper foil which is to be laminated with any of a variety of substrates through hot-pressing is subjected to nodular treatment. The nodular treatment is carried out so as to enhance adhesion between the copper foil and the substrate, on the basis of an anchor effect. Specifically, copper microparticles are formed on a surface of the copper foil through electrodeposition. Subsequently, a variety of surface treatments are further carried out in consideration of long-term storage stability of the copper foil and favorable adhesion to any of a variety of substrates formed of organic material.
In order to ensure favorable adhesion between a metallic copper foil and any of a variety of substrates formed of an organic material, a silane coupling agent has generally and widely been used.
In a copper-clad laminate, the silane coupling agent is present between a metallic copper foil and a substrate formed of an organic material. However, details of the silane coupling agent; e.g., the method of employment thereof, have not been sufficiently studied. Conventionally, there have been filed several patent applications with regard to a copper foil employing a silane coupling agent.
For example, Japanese Patent Publication (kokoku) Nos. 15654/1985 and 19994/1990 disclose a copper foil in which a zinc layer or zinc alloy layer is formed on a surface of the foil, a chromate layer is formed on the zinc or zinc alloy layer, and a silane coupling layer is formed on the chromate layer. Taking the entirety of the aforementioned patent publications into consideration, the feature of these patents is focused on drying treatment performed after formation of a chromate layer, and treatment with a silane coupling agent performed after drying. However, the present inventors have found that copper foil of expected performance cannot be obtained; i.e., performance and quality of copper foil varies greatly between lots, even though the copper foil is produced, on a trial basis, by means of the disclosed methods.
Japanese Patent Publication (kokoku) No. 17950/1990 discloses that treatment of copper foil with a silane coupling agent is able to improve resistance to hydrochloric acid, but does not particularly disclose the moisture resistance of copper foil. In recent years, problems have arisen which corresponds to trends toward formation of microwiring and multilayer printed wiring boards and in the field of interposer of semiconductor devices. Due to the employment of a copper-clad laminate having poor moisture resistance, delamination of multilayer printed wiring boards and poor pressure-cooker performance of packaged semiconductor devices has occurred.
Since a silane coupling agent layer is formed on an anti-corrosive layer comprising a zinc or zinc alloy layer formed on a copper foil and a chromate layer formed on the zinc or zinc alloy layer, there arise considerations such as combination of the silane coupling agent and the anti-corrosion layer, surface conditions of the anti-corrosion layer during adsorption of the silane coupling agent, and drying conditions. Thus, it is considered that no invention which brings out the maximum effect in the employed silane coupling agent has yet been accomplished.